4 th Esri Eastern Africa Education GIS User Conference Geospatial - - PowerPoint PPT Presentation

4th Esri Eastern Africa Education GIS User Conference

Geospatial Technology Based Regolith Mapping in the Western Metamorphic Terrain, Ethiopia. BY: Gizachew Kabite Date: 23/2016

Presentation outlines

• Introduction
• Methods and Materials

 Description of the Study Area  Methodology followed

• Results and Discussions
• Conclusions

Introduction

• Regolith: all weathering products accumulated on basement rocks overtime

(Crooks, 2002).

• Includes both in-situ weathered and transported.
• Regolith map can be used for several applications (Roach, 2003).
• Remote sensing can provide valuable information for regolith mapping and

characterization (Kruse et al., 2003; Perry, 2004).

• Band ratio and Principal Component Analysis are the common image analysis used

for information extraction (Yesou et al., 1993).

• Scarcely utilized for regolith mapping.
• Processed Landsat shows high degree of regolith-landform map.

Introduction

• Despite the valuable application of regolith mapping, very few research were done

so far globally but even no research were tried in Ethiopia. Objective of the Study

• To map and characterize regolith in the study area using the state-of-the-art so as to

provide baseline information particularly for groundwater potential and mineral exploration studies.

Materials and Methods

Description of the Study Area

·

• Western Metamorphic Terrain is one
• f the largest basement terrain in

Ethiopia.

• Covers about 85,000km2 total area.
• The area is endowed mainly with

gold and marble mineral resources.

Materials and Methods

Methodology

• DPCA(4/3 & 5/7) separate clay from vegetation; 5/4 highlights

ferruginous materials; 7+1 highlight silicate-rich materials; 5/7 indicate clay mineral and 3/1 indicate Iron-oxide.

Results and Discussions

Clay Minerals

·

• Mapped from 5/7 band ratio (Richards & Xiuping,

2006).

• Used to identify hydroxyl-bearing minerals
• High value indicates the presence of clay minerals

while low value shows unaltered rocks (Rawashdeh et al., 2006).

• The spatial variation of clay content in the area

revealed diversity of weathering intensity.

• The high value indicates active weathered area.
• Lower

value revealed areas with relatively unaltered rocks.

Results and Discussions

Iron-Oxide

·

• Recognized using ratio of band 3/1 (Druy, 1993; Richards

and Xiuping, 2006).

• High value indicates the presence of weathered iron

minerals while non-iron-oxide bearing zones (Rawashdeh et al., 2006).

• Iron-oxide

varies spatially within the study area revealing variation of weathering extent in the areas.

• Area with high clay content are shown to have low Iron-
• xide.

Results and Discussions

Ferrous Mineral

·

• Band

ratio

• f

5/4 is used to identify ferrous mineral((Papp, 2002).

• High value corresponds to high ferrous mineral while

low value indicates the presence of non-ferrous mineral.

• The spatial distribution of Ferrous minerals also

indicates the variation of weathering extent in the area.

• Area with high clay mineral also contain low ferrous

minerals.

Results and Discussions

Regolith Units

·

• Classified from color composite of DPCA band ratio

(4/3 and 5/7), 5/4 and 7+1 assigned as RGB.

• Each class has assumed to be with the same regolith

characteristics.

• Input for regolith land unit mapping.

Results and Discussions

Landform Map

·

• Output of slope and elevation classes overlay.
• Input in regolith land units mapping process.
• Most of the study area is lowland

Landform Slope% Elevation (m) Descriptions Foot slope 0-5 0-500 Lowest areas with flat slope Lowland 5-10 500-1000 Flat area with gentle slope Plain 10-15 1000-1500 Broad, flat & rolling slope Hilltops 15-30 1500-2000 Raised part with steep slope Mountains >30 >2000 High rock land with very steep slope.

Results and Discussions

Regolith Land Unit Map

·

• Land units with relatively homogenous regolith character

and similar landforms.

• Each with specific slope and similar weathering intensity.
• But not necessarily show uniform regolith materials.
• Typically show associations where landform and regolith

attributes are linked.

• The purity of the units depends on the mapping scale

used.

Conclusions

• The integrated Geospatial Technologies are found to be an indispensable approach in

regolith mapping.

• Band ratio and DPCA techniques are vital in providing regolith and weathering information.
• Color compositing band ratio are effective in showing signatures of various regolith units.
• Despite the geology of the area is the same, five different units are identified.
• Revealed that degree of weathering is controlled by other factors like rainfall, vegetation

and temperature in the study area.

• By accounting the effect of topography, five Regolith Land Units are also identified and

mapped.

• Each RLUs could possibly show similar landform and regolith characteristics but the purity of

the unit depends on the mapping scale.

• Generally, if supported by detail field data, the methodology followed in this research is

effective in mapping regolith with time and cost effectively.

THANK YOU!